Process for the preparation of neopentyl glycol

ABSTRACT

The invention relates to a process for the preparation of neopentyl glycol by hydrogenation of hydroxypivaldehyde (HPA) in the presence of hydrogen and a hydrogenation catalyst at an elevated temperature. According to the invention, hydroxypivaldehyde is hydrogenated in the presence of a nickel-containing catalyst and at a temperature below 100° C. in a liquid phase containing a solvent an amount of 1-70% by weight and water in an amount of 0-15% by weight. Aliphatic alcohol or ether or a mixture thereof is used as solvent.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/FI98/01031 which has an Internationalfiling date of Dec. 30, 1998, which designated the United States ofAmerica.

The invention relates to a process for the preparation of neopentylglycol. More precisely, the invention relates to a process for thepreparation of neopentyl glycol by hydrogenating hydroxypivaldehyde witha hydrogenation catalyst at an elevated temperature.

Neopentyl glycol and other corresponding alcohols are importantintermediates, for example, in the production of various syntheticresins, such as acrylic resins polyester resins, polyurethane resins,alkyl resins and polycarbonate resins. These alcohols are also used inthe preparation of plasticizers, synthetic lubricants, surfactants, etc.

Neopentyl glycol and other corresponding alcohols have conventionallybeen prepared by two processes. In one process, formaldehyde andaldehyde are allowed to react with a strongly alkaline catalyst, such assodium hydroxide, potassium hydroxide or calcium hydroxide, to formalcohol, such as neopentyl glycol. However, the disadvantage of thisprocess is that large amounts of sodium formate are formed as aby-product. The process is therefore not suitable for a commercialprocess unless an economically profitable use is simultaneously foundfor the formate.

In the other process, the aldolisation reaction of formaldehyde andaldehyde is carried out in the presence of an amine catalyst, inparticular triethylamine. Neopentyl glycol is obtained, for example, byreacting formaldehyde and isobuyraldehyde in the presence oftriethylamine, whereby hydroxypivaldehyde is formed as the main product.This can further be hydrogenated, whereby the desired neopentyl glycolis obtained as the end product. The aldolisation reaction can be carriedout also by using an anion exchange resin as a catalyst.

Many types of catalysts have been proposed as the hydrogenationcatalyst. U.S. Pat. No. 4,250,337 proposes as a catalyst copper chromitewith barium as its promoter. In U.S. Pat. No. 4,855,515, the catalystused is a mixture of copper oxide and copper chromite, with manganeseoxide as promoter. In EP patent 343 475, a mixed catalyst made up ofplatinum, ruthenium and tungsten is used as the catalyst.

It has been observed that particularly nickel catalysts do not functionsatisfactorily at relatively low temperatures below 100° C. Thehydroxypivaldehyde conversion and NPG conversion obtained do not reach alevel adequate for commercial processes. Only with certain preciousmetal catalysts relatively good results have been achieved. Thus, forexample, according to EP patent 343 475, a catalyst containing platinum,ruthenium and tungsten is used even at a temperature of 80° C. Assolvent, water or a mixture of water and alcohol is used.

When nickel catalysts are used, the high hydrogenation temperaturecauses an intense increase in the amount of by-products, particularlyneopentyl glycol-monoisobutyrate and hydroxypivalyl hydroxypivalate.These harmful by-products are difficult to separate from the desiredneopentyl glycol, especially neopentyl glycol monoisobutyrate.Furthermore, the profitability of the manufacturing process is reducedas the selectivity decreases due to the increase in the amount ofby-products. Additionally, when lower reaction temperatures are used,significantly larger amounts of the catalyst are needed, which leads tolarger process volumes, and also reaction times are markedly longer,which factors render the process less suitable on an industrial scale.

The hydrogenation of hydroxypivaldehyde is usually carried out in asolvent phase. the solvent used being conventionally water. In thehydrogenation reaction, water reduces selectivity. In addition, theusable lifetime of nickel catalysts decreases significantly since a highwater content tends to destroy the particle structure of the catalysts.

Thus there clearly exists a need for an improved process with superiorselectivity for the preparation of neopentyl glycol with very low levelsof impurities, by hydrogenation of hydroxypivaldehyde at lowtemperatures using commercially available nickel catalysts.

The invention relates to a process for the preparation of neopentylglycol by hydrogenating hydroxypivaldehyde (HPA) using a nickelcatalyst, in which process the amount of by-products is extremely small.Another embodiment of the invention is the manufacturing process ofneopentyl glycol (NPG) where a high HPA conversion and a high NPGselectivity are obtained.

According to the invention. it has been surprisingly observed that theafore-mentioned objectives can be achieved by hydrogenatinghydroxypivaldehyde at low temperatures below 100° C., and by usingalcohol or ether or a mixture thereof as solvent, and by limiting theamount of water present in the hydrogenation solvent to less than 15% byweight.

In the process according to the invention, hydroxypivaldehyde used as afeed material can be prepared according to any method available. Aconventional process for the preparation of hydroxypivaldehyde is toperform an aldolisation reaction where formaldehyde and aldehyde arecaused to react in a so-called aldolisation reaction in the presence ofan amine catalyst, in particular triethylamine. Another. even morerecommendable process, is to perform a corresponding aldolisationreaction with a weak anion exchange resin acting as an aldolisationcatalyst.

In the aldolisation step. formaldehyde and aldehyde are contacted withan anion exchange resin at a molar ratio of 10:1-1:10, preferably5:1-1:5. The reaction can be carried out at a temperature of 15-100° C.When using an anion exchange resin, the upper limit for the temperatureis set by the thermal resistance of the anion exchange resin used. Thealdolisation reaction can be carried out as a batch process or asemi-batch process or preferably as a continuous process.

As a catalyst, weakly basic anion exchange resins are used in which thefunctional group is a primary amine (—NH₂), a secondary amine (—NHR,where R is an alkyl or an aryl) or a tertiary amine (—NR₂ where R is asabove) or mixtures thereof. The resin matrix used can be, for example,condensation products of epichlorohydrine with amine or ammonia,phenolic resins, acrylic resins, or styrene copolymers, such aschloromethylated styrene-divinylbenzene copolymer.

The aldolisation reaction can also be carried out by using solvents.Suitable solvents include, among others, water and various alcohols,such as methanol, ethanol, n-propanol. isopropanol, n-butanol andisobutanol, or mixtures thereof, the amount of which in the reactionsolution may vary within a range of 0-50% by weight. preferably within arange of 0-30% by weight.

After the aldolisation step and, if necessary, after the separation ofthe aldolisation catalyst, the reaction mixture is fed without anyfurther separation measures directly to hydrogenation. According to theinvention, a catalyst comprising nickel is used as the hydrogenationcatalyst. The amount of nickel in the catalyst may be 60-99% by weight.The catalyst may also contain chromium and the amount of chromium may be1-40% by weight. The catalyst may also be combined with a suitablecarrier which can be an inorganic oxide, such as silica. Said catalystsare conveniently commercially available, and no special catalysts areneeded.

According to the invention, the hydrogenation is carried out at a lowtemperature in the presence of a solvent. As solvents, alcohols orethers or mixtures thereof are used. Suitable alcohols include, forexample, methanol, ethanol, propanol, butanol, hexanol, octanol,neopentyl glycol and butyl ether or dioxane. The amount of the solventmay vary within a range of 1-70% by weight, but preferably within arange of 10-50% by weight. The purpose of the solvent is to increase thesolubility of hydroxypivaldehyde in the liquid phase, since at lowoperating temperatures the solubility of HPA is reduced wherefore it mayprecipitate in the reaction solution. This can occur particularly whenthe conversion during the aldolisation step is hitch and thus the HPAconcentration is high in the reaction mixture.

According to the invention, the hydrogenation is performed at atemperature below 100° C., preferably 60-90° C. The hydrogenationpressure may vary within a range of 1-200 bar, preferably 10-80 bar. Theselectivity of the hydrogenation reaction is at least 98% due usinglower operating temperatures. Additionally formation of ester impuritiesis practically elimited and retro-aldolisation reaction is avoided thusincreasing the overall yield of the process. In the case when thealdolisation reaction is carried out using a weak anion exchange resinas an aldolisation catalyst aid-free feed is obtained and mild operationconditions in the hydrogenation step are suitable, because formation ofester impurities and acetals is avoided and there is no need forhydrogenolysis of ester impurities at high temperatures. Thehydrogenation may be carried out as a batch or a semi-batch process, orpreferably as a continuous process.

In the hydrogenation, it is important that the feed solution contains aslittle water as possible. Thus the amount of water in the solution to behydrogenated is 15% by weight at the most, preferably lower, or thereaction mixture to be hydrogenated does not contain any water at all.Excess water may cause an increase in the quantity of by-products and areduction in the selectivity and conversion in the formation ofneopentyl glycol.

After the hydrogenation reaction, the desired alcohol, i.e., neopentylglycol, is separated from the reaction mixture by a suitable method, forexample, by distillation, and the solvents used may be recycled to thehydrogenation and/or aldolisation step.

The hydrogenation of hydroxypivaldehyde in the presence of a catalystcomprising nickel at low temperatures of 100° C. or below is especiallysuitable for larger. industrial scales because of the improvedselectivity and good conversion. Surprisingly small amounts of thecatalyst comprising nickel are needed and this results in a need forsmaller reaction volumes. thus rendering the process more economical.

In the following, the invention is described in more detail withreference to the accompanying examples which are nevertheless notintended as limiting the invention.

EXAMPLE 1

Hydroxypivaldehyde (HPA) was hydrogenated in the presence of a Ni/Crcatalyst in a Parr-reactor with a volume of 300 ml. The nickel contentof the catalyst was approx. 69% by weight and the chromium contentapprox. 13% by weight. Silica was used as the carrier agent of thecatalyst. The feed solution comprised unpurified hydroxypivaldehyde inan amount of 160 g obtained by an aldolisation reaction catalysed by aweak anion exchange resin. Hydrogenation was carried out at atemperature of 70° C. and at a pressure of 70 bar using methanol as asolvent. The hydrogenation time was 240 minutes.

The properties of the feed solution and the produced reaction mixtureare presented in the accompanying Table 1.

TABLE 1 Compound Feed (wt-%) Product (wt-%) HPA 33.0 3.0 NPG 0.08 30.5HPHP 0.08 0.17 NPG-mibut 0.04 0.06 IBAL 4.34 0.11 MeOH 50.4 50.0 IBUOH —4.21 H₂O 11.8 11.8 HCOOH — — Others 0.26 0.15

HPA=hydroxypivaldehyde, NPG=neopentyl glycol, HPHP=hydroxypivalylhydroxypivalate, NPG-mibut=NPG-monoisobutyrate, IBAL=isobutyraldehyde,MeOH=methanol, IBUOH=isobutanol, HCOOH=formic acid, Others=formaldehydeand unidentified compositions.

NPG selectivity was 98.5% calculated from the product analysis. HPAconversion was 91% calculated from the product analysis.

The example shows that hydrogenation can be carried out even at 70° C.with good yield when a nickel catalyst is used as a catalyst and alcoholas a solvent and when the amount of water is less than 15% by weight ofthe feed solution. The quantity of by-products was remarkably small.

EXAMPLE 2

Hydrogenation of HPA was performed in a continuous trickle bed reactorand experiment arrangements are described in the following:

Reactor: Tube reactor, diameter 16 mm, length 400 mm Catalyst: Ni/Cr onsilica support, total Ni-content 69 wt-% (Ni, NiO), total Cr-content 13wt-%, the catalyst was crushed to an average particle size of 1 mm Feed:Crude HPA from aldolisation without any purification operations,aldolisation catalysed by a weak anion exchange resin Solvent: methanolCatalyst 6 g, silicon carbide was used as inert diluent amount: materialabove and below the actual catalyst bed Liquid 12 g/h feed rate:Temperature: average bed temperature 70° C., temperature measured at 3different points along the catalyst bed Pressure: 70 bar (abs) Spacevelocity WHSV = 2 Operation mode: The feed was pumped continuouslythrough the reactor and collected in a cooled product drum, excess ofhydrogen was used measured with a gas flow meter at a gas outlet streamfrom the product drum. The reactor temperature was controlled usingelectric heaters around the reactor shell.

The properties of the feed stream and product stream compositions insteady state conditions are shown in the following table 2.

TABLE 2 Compound Feed (wt-%) Product (wt-%) HPA 34.8 2.34 NPG 0.16 33.08HPHP 0.11 0.19 NPG-mibut 0.03 0.03 IBAL 2.66 0.13 MeOH 49.7 49.9 IBUOH 02.43 H₂O 11.7 11.7 HCOOH 0.02 0.02 Others 0.82 0.18

NPG selectivity was 99.7% calculated from the product analysis.Conversion of HPA was 93.2%, which can be increased by decreasing thefeed rate and thus the space velocity WHSV.

What is claimed is:
 1. A process for the preparation of neopentyl glycolwhich comprises hydrogenating hydroxypivaldehyde (HPA) in the presenceof hydrogen and a hydrogenation catalyst at an elevated temperature,wherein the hydrogenation of hydroxypivaldehyde is carried out in thepresence of a catalyst containing nickel or nickel-chromium and at atemperature below 100° C. and under a pressure of 10-80 bars in a liquidphase comprising solvent in an amount of 1-70% by weight and water in anamount less than 15% by weight, wherein said hydroxypivaldehyde isobtained by aldolization of formaldehyde and isobutyraldehyde with aweakly basic anion exchange resin acting as an aldolization catalyst. 2.The process according to claim 1, wherein the solvent is an aliphaticalcohol or ether or a mixture thereof.
 3. The process according to claim1, wherein the solvent is methanol, ethanol, n-propanol, isopropanol,n-butanol or isobutanol, or a mixture thereof.
 4. The process accordingto claim 1, wherein the solvent is used in an amount of 10-50% by weightof the reaction mixture going to the hydrogenation.
 5. The processaccording to claim 1, wherein the hydrogenation catalyst containschromium in an amount of 1-40% by weight.
 6. The process according toclaim 1, wherein inorganic oxide is used as a carrier of thehydrogenation catalyst.
 7. The process according to claim 1, wherein thealdolization catalyst is a weakly basic anion exchange resin, in whichthe functional group is a primary amine (—NH₂), a secondary amine (—NHR,where R is an alkyl or an aryl) or a tertiary amine (—NR₂ where R is asabove) or mixtures thereof.
 8. The process according to claim 6, whereinsaid inorganic oxide is silica.